"Greater London is further divided into 32 London boroughs, each governed by a London Borough Council, and the City of London, which is governed by the City of London Corporation. In the London boroughs the legal entity is not the Council as elsewhere but the inhabitants incorporated as a legal entity by royal charter (a process abolished elsewhere in England and Wales under the Local Government Act 1972). Thus, a London authority's official legal title is "The Mayor and Burgesses of the London Borough of X" (or "The Lord Mayor and Citizens of the City of Westminster"). In common speech, however, "The London Borough of X" is used."

So I think the sign should say:The London Borough of Newhamor perhapsLondon Borough of Newham